Abrasive



Patented Dec. 10, 1940 PATENTf -OFFICE.

anassrvn I Arthnr J. Weinig, Golden, can.

No Drawing. Application January 16, 1939, Serial No. 251,132

3 Claims. (01. 51401) This invention relates to a precision abrasive and to the process of manufacturing the same.

The finest abrasive materials at present on the market are either too coarse, too evenly graded, or too harsh to produce a microscopically sharp,

cutting edge of high precision; or else they are so soft and fine as to require great time and labor to produce a satisfactory cutting edge. Present abrasives are also usually incorporated in agreasy, oily, or waxy binder which causes glaz-- ing of the honing surface so that uniformity of edge is impossible.

Thprincipal object of this invention is to produce an extremely finely divided abrasive of fast but tempered cutting qualities which will be suitable for sharpening precision instruments of the type which require an extremely sharp cutting edge such as surgical instruments, microtome knives, razors, etc. and to provide a process for manufacturing the abrasive which will be simple and economical and which will produce a uniformly excellent product.

Another object of the invention is to provide an abrasive in which all greasey, oily, or oleaginous binders are eliminated so that the final product will be a dry, fine abrasive in powdered or stick form which will not be subject to self-classification, separation, or stratification and which will permanently maintain a uniformity of material throughout an entire batch without the objectionable features of a greasy or waxy substance.

A still further object of the invention is to provide an abrasive which will cling uniformly over the entire honing surface without the use of greases, waxes, oils, or soaps. In fact, in the present invention, in the final product there is no water, salt, rosin, wax, oil, soap, or other similar vehicle for binding purposes. These have been eliminated to avoid their undesirable lubricating properties yet all their desirable qualities have been maintained by so forming the product that it acts as a self-binding and self-clinging product, and one that can be'operated without glazing.

One of the principal uses for the product has been found to be the grinding of surfaces such as mineral surfaces, meteroric surfaces, microscope slides, and the like for mlcroscopicstudy.

For such a study any surface abrasions or scratches, would be objectionable due to the great magnification thereof and for this purpose none of the ordinary ginding compounds would be of any value. The improved material, however, is not limited to this specific use but has been found to be of great value'in sharpening precision cutting blades such as microtome blades to an exceedingly fine smooth cutting edge. Abrasives such as the finest grades available on the market of optical emery, flours of silicon 6 carbide, boron carbide, tungsten carbide, alumina and garnet, are fast, cutting. The main grain sizes range from to 20 microns. They do not however produce the microscopically polished surface necessary for microtome or microscopic l0 purposes. On the other hand, the finer soft abrasives, such as the metallic oxides generally known as crocus, red and black rouge, etc. do produce a highpolish but the cutting action is very slow and they are incapable of removing 15 the bilge or roundness that develops along the sides of cutting edges through long use. This invention comprises a dry abrasive powder-having all the desirable qualities of a harsh" abrasive combined with all, the desirable qual- '20 rials of differing hardness and differing coarse.-

ness, so arranged that the preponderance of the 25 coarser grains'will be of the harder constituents. while the preponderance of the finer grains will be of the softer constituent. The softer constituent is ground to a'sufiicient fineness to act as a dry binder for maintaining the coarser grains 80 evenly, uniformly, and. permanently distributed throughout the product and so that its excessive fineness will impart a clinging or adhesive action to cause the composition to adhere to surfaces in the nature of the clinging action ofdry s5 chalk. r v

. Process The finest available hard abrasive products now obtainable on .the market such as silicon o carbide or/and aluminum oxide hereafter called the abrasive is subjected to wet or dry grinding in a pebble mill. The grinding mediaconsists' of pebbles of flint or chalcedony. During the grind-- ing, the-flint pebbles wear down more rapidly than the harder abrasive and produce a pulp .con-

' sisting of an abundance of extremely fine siliceous powder mixed with a lesser amount of fine rains of the harder abrasive.

The grinding reduces amajority of the brigmicrons. All of the grain are rejected and if the amount of flint microns or less is too great, a portion of it is also well agitated.

sizes above 20 microns of 5 rejected.

The powder remaining after the above rejections has all the rapid cutting qualities 0! the silicon. carbide or aluminum oxide and in addition the harshness has been removed or tempered by the buffer action of the {fine flint grains. The

powder thus produced cuts rapidly and yet maintains smooth, highly polished, surfaces which can be brought to an bilge. v v A To prevent any possibility of segregation or stratification and to further. the adherence of the powder to a honing surface such as a leather strop and to otherwise improve the soft, yet'rapld, cut ting action of the product, it is preferred to incorporate the combined powders into a dry gel, preferably insoluble copper hydroxide, although the insoluble hydroxides of aluminum, zinc, and iron and vegetable gums are also suitable. The method of applying the gel is preferably as follows: I

First decant The combined, ground abrasive is agitated in water in a shallow tank. If impurew'ater or other causes produce flocculation a suitable deflocculating agent such as tannic acid is added. The pulp is allowed to repose quietly until by test or calcuiationall grain sizes above 5 microns have settled 7 below a pre-determined level in the tank. The

pulp above this levelj'is then siphoned or decanted oil. The pulp in the decant will now contain the major portion, but not all, oftheparticles of 5 microns or less. A solution of copper sulfate is now added to the latter pulp and the mixture is 'An alkali, suchas a'sodium hydroxide solution, is nowcarefully added with continued agitation until the copper is substantially all precipitated as copper'hydroxide inthe pulp after which the pulp is allowed to repose quietly. The large flocs of gel inwhich the particles of the abrasive and flint are entrapt now settle rapidly and, as soon as settlement is complete, the

" supernatant clear water is siphoned off and the residual thickened pulp is filtered and dried.

The product thus derived,. h'erein' referred to as the first decant, will" be largely fine flint (5 microns or less) It is reserved for blending with a second decant material.

w" at The coarser pulp remaining in the original tank, below the decanted level (exceeding 5 microns) is again agitatedin water, a deflocculant is added if necessary, and is then allowed to repose and settle until by test or calculation the particles larger than 20 microns have settled out below a predetermined level. The pulpabove this level is then decanted and treated with copper sulfate, alkali, settled, filtered anddried as was done in the first decantation. This second decantation is repeated in all detail, usually four times, until continued decantations do not yield substantial amounts of sized material below20 microns size. We now have a product consisting in the main of the abrasive flour 0! less than 20 microns grain extremely thin edge without size which will be designated the "second decant."

. Final combination The first and second decants are now intimately intermixed in the dry state to produce the final abrasiveproduct. The mixture is carefully tested and controlled by placing samples on a smooth, level, leather strap and then stropping a section of microtome blade. If there is'a harsh cutting action; which can be detected after a little trial and experience, an additional amount of the first decant is added to the compound until the test shows the harshness is eliminated. The

- final product is then moistened, thoroughly re- Experience will in time teach one to so regu-,

late the time of grinding that the proper proportion of fine flint material will be produced in the pebble mill so that the initial separation of the 5 micron sizes in aflrst decant will not be necessary and all decants then can be conducted simply for the separation of material coarser than 20 microns.

The excess fine flint which has been rejected after the grinding will contain a .certain amount.

of fine carborundum which, of course, would be valuable in the final product. I

This carborundum may be separated from the flint and recovered by froth flotation in water. Pine oil or cresylic acid may be used as a frothing reagent and any suitable collecting reagent such as a fatty'acid or its soaps may be used. It has been found that carborundum grains up to 35' mesh can be readily removed from the flint by this froth flotation method.

While a preferred form of product has been described in some detail for use in sharpening instruments requiring a very fine cutting edge to-,

gether with the preferred process of producing the same, it is to be understood that the invention is not limited to the precise ingredients nor to the precise procedure described except in sofar as such limitations are included in the appended claims inwhich it is the intention to claim all novelty inherent in the invention with due regard to the prior art. d

Having thus described theinvention what is; claimed and desired secured by Letters Patentis:

1. A dry abrasive for fine grinding comprising: a dry mixture of powdered silicon carbide, powdered flint, and precipitated copper hydroxide the grain size of the silicon carbide not exceedin 20 microns. and the grain size of the flint not ex-i ceeding 5 microns in size.

2. A dry abrasive for line grinding comprising:

a dry mixture of powdered silicon carbide, powdered flint, and precipitated copper hydroxide. I

3. An abrasive for fine grinding comprising: powdered silicon carbide; powdered flint; and a precipitated metal hydroxide.

ARTHUR J. WEINIG. 

